docs: clarify what str.split does

The wording was a bit confusing and misled at least one person into
thinking it behaved like `str.replace('c', '')` operating on the entire
line. Tweak the wording to be more precise and avoid this confusion.

docs/markdown/Syntax.md

@@ -252,13 +252,13 @@ s = s.replace('as', 'are')
 #### .strip()
 
 ```meson
-# Similar to the Python str.strip(). Removes leading/ending spaces and newlines
+# Similar to the Python str.strip(). Removes leading/ending spaces and newlines.
 define = ' -Dsomedefine '
 stripped_define = define.strip()
 # 'stripped_define' now has the value '-Dsomedefine'
 
 # You may also pass a string to strip, which specifies the set of characters to
-# be removed.
+# be removed instead of the default whitespace.
 string = 'xyxHelloxyx'.strip('xy')
 # 'string' now has the value 'Hello'
 ```

docs/yaml/elementary/str.yml

@@ -61,7 +61,10 @@ methods:
 
 # str.strip()
 - name: strip
-  description: Removes leading/ending spaces and newlines from the string.
+  description: |
+    Removes leading/ending characters from the string.
+
+    By default the characters to remove are spaces and newlines.
   returns: str
   example: |
     ```meson
@@ -75,7 +78,8 @@ methods:
     strip_chars:
       type: str
       since: 0.43.0
-      description: All characters in this string will be stripped.
+      description:
+      description: Instead of whitespace, strip all the characters in this string.
 
 # str.to_lower()
 - name: to_lower